With regard to WDM networks, in future there will be fully optical (also referred to as photonic), transparent domains. In order to increase the transmission capacity of the individual channels of a WDM or DWDM signal (dense wavelength division multiplexing) it is possible to employ the polarization multiplex technique in such a network. Two differently polarized optical signals whose directions of polarization are normally orthogonal can be transmitted on one wavelength of a channel. Add/drop modules or optical cross-connectors are currently used for the through-connection, addition and/or feeding out of channels in a network element connected to the optical network. These known network elements are simply capable of selectively switching different wavelengths as their smallest granularity. Thus, when using these network elements in the case of optical networks with polarization multiplex, two signals which are situated on one wavelength are always switched.
In addition to wavelength granularity, current add/drop modules can also switch wavelength group granularity. This means that for example a plurality of channels from the optical network with separate wavelengths are coupled instead of a single channel. The wavelength-selective switching takes place in an additional switching device which is connected to that used for wavelength group switching.
The normal cross-connectors have the same wavelength granularity and wavelength group granularity as the add/drop modules and also the patch panel granularity which is based on a switching of all or a plurality of channels or of one channel of a WDM signal from one fiber of the optical network to another fiber.
A cross-connector having a first switching device for patch panel switching (fiber routing switch FR) of signals is described in EP 1 162 855 A1, whose inputs and outputs are linked to outputs and inputs respectively of a second switching device for wavelength switching (wavelength routing switch WR) of channels of a WDM signal. This cross-connector is not however suitable for switching polarized signal components of a polarization multiplexed signal.
A polarization multiplex switch is known from EP 1 137 308 A2, to whose input one channel with two orthogonal polarization states is fed. A regulated polarization controller regulates the two polarization states of the channel in such a way that two signals having orthogonal directions of polarization are separated by a polarization beam splitter. The regulation of the polarization controller is used in order to optimize the mapping of the two directions of polarization of the outgoing signal from the polarization controller on the separating characteristics of the polarization beam splitter. This polarization demultiplexer forms a drop switching of one of the two orthogonal linearly polarized signals. In addition, the remaining second orthogonal linearly polarized signal passes through a polarization beam coupler tuned to its direction of polarization where it is combined with a new external signal. The new external signal exhibits a direction of polarization which is orthogonal to the direction of polarization of the signal from the polarization beam splitter.
A switch is also described here in which a WDM signal is fed into a wavelength demultiplexer in order to separate its channels. Some channels are fed into a plurality of add/drop modules and other channels are fed into polarization switches. This switch is therefore not optimally suited in the case of a dynamic optical network having a variable number of channels and/or having variable transmission properties for the channels such as polarization and/or wavelength multiplex because a further item of information from each incoming new channel would be required in order to perform appropriate switching.